package com.hnevc.xiewenguang;

import java.util.Scanner;

public class Example01 {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        double x1=sc.nextDouble();
        double y1=sc.nextDouble();
        double x2=sc.nextDouble();
        double y2=sc.nextDouble();
        double ab=0.0;
        ab=Math.sqrt(Math.pow(x1-x2,2)+Math.pow(y1+y2,2));
        System.out.printf("%.2f",ab);
    }
}
